The present invention relates to a radio telephone apparatus which performs voice or data communication through radio transmission and receipt operations and includes a voice coil used for effecting magnetic coupling with a pickup coil provided in a hearing aid used by a hearing-impaired person, as well as to a method for controlling electric current consumption of the radio telephone apparatus.
Some wired telephones have a voice coil for the benefit of a hearing-impaired person, and such a voice coil is also applied to a radio telephone apparatus. A telephone feeds, to the voice coil, an electric current corresponding to a voice, so that a magnetic field is generated. In the meantime, some hearing aids used by the hearing-impaired persons have pickup coils. The pickup coil magnetically couples with the voice coil provided in the telephone, thereby a voice output from the telephone is transmitted to the hearing aid. As a result, the voice output from the telephone can be transmitted without being affected by ambient noise, in contrast with the hearing aid that picks up a voice by a microphone.
In relation to the radio telephone apparatus, in the case of a portable cellular phone used on a wide frequency band, voice or data are transmitted by exchanging a radio wave with a cell site. In the case of a cordless telephone used in a house, voice or data are transmitted by exchanging a radio wave between a base unit and a handset.
A portable cellular phone which is an example of the radio telephone apparatus includes a transmission section and a receiving section for effecting radio communication. The transmission section is a circuit for transmitting a radio wave to the cell site. When a radio wave is transmitted, a large quantity of current flows from a battery, which serves as a power source, into the circuit. The receiving section is a circuit for receiving a radio wave from the cell site. When a radio wave is received, an electric current flows into the circuit. By timewise changes in the flowing electric current, a magnetic field originates from surroundings of the circuit of the transmission section or the circuit of the receiving section.
On the assumption that the portable cellular phone performs transmission and receipt by a time-division slot scheme formed from a transmission slot, which is to be a duration in which a radio wave is transmitted to a cell site, and a receiving slot, which is to be a duration in which the cell site transmits a radio wave, changes in the magnetic field appear every period of the time-division slot.
Accordingly, the magnetic field, which is noise developing every period of a time-division slot, is magnetically coupled with the pickup coil provided in the hearing aid, and the noise is superimposed on the voice as a hum that develops every period of the time-division slot. This hum makes it very difficult for the heating-impaired person to hear a voice. Especially, an amplifier for amplifying the signal, which will become the source of a radio wave, consumes a large amount of electric current, and hence time-wise changes in the electric current for a transmission slot are great, so that the level of development of a magnetic field also becomes greater correspondingly.
A radio telephone apparatus which dampens the influence of such a timewise-varying magnetic field is described in U.S. Pat. No. 5,960,346. The radio telephone apparatus described in U.S. Pat. No. 5,960,346 has a smoothing capacitor connected in parallel with a transmission section. Sharp variations in electric current can be dampened by feeding an electric current from the smoothing capacitor to the transmission section, thereby reducing the level to which the magnetic field develops.
The smoothing capacitor used in the radio telephone apparatus described in U.S. Pat. No. 5,960,346 must have a time constant which is longer than that of a time-division slot. Hence, a capacitor of comparatively-large capacitance is used. Miniaturization and weight reduction of the radio telephone apparatus are desired so that the radio telephone apparatus can be easily carried. Difficulty is encountered in ensuring a space used for mounting circuit components. For these reasons, mounting of a smoothing capacitor of large capacitance is difficult.